2.3 Carbohydrates and lipids

Question 1

What are the 4 functions of carbohydrates?

Answer 1

1) Energy source and storage - glucose (source) – starch (plant storage)/glycogen (animal storage)
2) Structure - cellulose and chitin
3) Molecular recognition on cell surfaces
4) form part of larger molecules (nucleic acid and glycolipids)

Question 2

What are monosaccharides? What is the basic formula? What are the similar properties they share?

Answer 2

Cn(H2O)n
They are the simplest form of sugars and the most basic unit (monomers) of carbohydrates.

Properties

• soluble in water
• sweet tasting
• can form crystals

Question 3

What is glucose?

How many carbons does it have? Energy source from where? Solubility? What can it form?

Answer 3

• Monosaccharide - simple sugar
• Has 6 carbons - Hexose sugar
• Carbohydrate
• Energy source from respiration
• Soluble in water
• Forms chain and ring structures - useful building block

Question 4

What are other examples of hexoses (isomers of glucose)?

Answer 4

Isomers - same molecular formula but different structures

Galactose and fructose

Question 5

What is the breakdown of glucose called? How is it done?

Answer 5

Glycolysis.

Animals and plants have enzymes that can break down alpha glucose (but not beta)

Question 6

What does condensation of two alpha glucose monosaccharides form?

Answer 6

Maltose disaccharide

Question 7

What is the bond that is formed between two alpha glucose or between maltose? Where is the bond?

Answer 7

A C 1-4 glycosidic bond is formed (covalent)

Question 8

What is polymerisation?

Answer 8

Subsequent condensation reactions that build up a polysaccharide chain

Question 9

How can maltose breakdown back into two alpha glucose?

Answer 9

Hydrolysis of the glycosidic bond. Use H20 to replace and seperate the bonds and groups.

Question 10

What are disaccharides? What are the 3 disaccharides made of?

Answer 10

Disaccharides are double unit sugar is composed of two monosaccharides held together by an oxygen bond created during a process known as condensation reaction.

Common disaccharides

• Glucose + fructose -> sucrose
• Glucose + galactose -> lactose
• Glucose + glucose -> maltose

Question 11

What is ribose?

What sugar is it? Is it a monosaccharide or a disaccharide? Where can it be found?

Answer 11

• Ribose is a 5 carbon sugar and is known as a pentose sugar
• Ribose also a monosaccharide
• Ribose can be found in the nucleic acid RNA (ribonucleic acid)

Question 12

What are the similarities and differences between glucose and fructose? (2)

Answer 12

Both have H and -OH

Glucose have 6C rings, fructose has 5C

Question 13

What are polysaccharides? What are three examples?

Answer 13

They are many monosaccharides bounded together

• starch
• glycogen
• cellulose

Question 14

What are two particular alpha glucose polysaccharides and where is it used? What is alpha glucose mainly for?

Answer 14

Alpha = energy store

Starch (in plants) - make up amylose (20%) and amylopectin (80%)

Glycogen (animals) - storage of glucose (branched, compact, plenty of sites where hydrolysis of glycosidic bonds to release glucose (for respiration)

Question 15

What is starch? What is it made out of? What are the two main types and the location of their bonds? Solubility? Good for storage? Where is it found?

Answer 15

• Made up of alpha glucose monomers
• Consists of 2 mains types:
  unbranched amylose (20%) - C1-4 bonds
  branched amylopectin (80%) - C1-4 and C1-6
• Insoluble so does not affect osmosis or diffusion
• Good for storage as compact making it energy dense
• Glucose storage in plant
• Hydrolysed to release glucose monomers which are used in respiration to release energy

Question 16

What is the structure of amylose?

Where are the bonds? What’s the length? What shape does it take and what holds the shape?

Answer 16

Amylose is an unbranched component of starch, formed from 1-4 linkage of alpha glucose molecules.
The chain of 1-4 linkages formed is quite long, and may wind up into a helix which is held together by internal H bonds.

Question 17

What is amylopectin?

Branched? How quick is it to hydrolyse, why? Where are the bonds?

Answer 17

• Highly branched structure
• Can be hydrolysed more quickly than amylose as more places available for enzymes to attach and cut to release glucose
• alpha glucose molecules joined by alpha 1-4 glycosidic bonds with alpha 1-6 branches every 20-30 monomers
• Stored, then hydrolysed if need a supply of energy

Question 18

What is glycogen made up of? Branches? where are the bonds? Compact? Solubility? Accessibility? Glucose storage where?

Answer 18

• Made up of alpha glucose
• Lots of branches (more than amylopectin in starch) - has C1-4 glycosidic bonds to create chains and C1-6 glycosidic bonds create branches every 7 to 11 monomers
• Extremely compact structure - energy dense storage
• Insoluble - does not affect osmosis or diffuse out of cells
• Enzymes can access multiple sites due to branches so that hydrolysis can easily occur and glucose can be easily obained
• Glucose storage in animals - liver and muscle

Question 19

What are two particular forms of polysaccharides? Where can it be found?What is beta glucose mainly for?

Answer 19

1) Cellulose (in plants)
2) Chitin (in fungi and insects)

beta glucose is mainly for structural purposes

Question 20

What is the difference between alpha and beta glucose? How do beta glucose form chains? Where are the glycosidic bonds for beta?

Answer 20

One of the H to -OH groups are flipped.
Beta glucose forms in straight chains and in order to achieve this, every second beta glucose is rotated 180˚ vertically so that the -OH groups of two beta glucose are align.

C1-4 glycosidic bonds

Question 21

What is cellulose?
What is it made up of?
Where are the links/bonds?
Branched?
How are hydrogen bonds formed in this structure?
How do cellulose fibres form? What do microfibrils provide?
Easy to hydrolyse/digest?
How does it resist bursting?
Where is it found?

Answer 21

• Made up of beta glucose chains - joined with C1-4 links
• Unbranched chains joined with hydrogen bonds
• H bonds form rigid cross links and bind chains into microfibrils
• Microfibrils provide structural support in plant cell walls
• Not hydrolysed/digested easily - few organisms have cellulose enzyme
• Provide turgor pressure - resists bursting
• Found in plants - structure

Question 22

What role does cellulose play in plant cell walls? How does it affect leaves and plant cells?

Answer 22

It provides rigidity, prevents plant cells from bursting when water enters via osmosis - plant cells become turgid.

Turgid cells can push against each other and enable leaves to keep their shape - increase SA.

Question 23

What are lipids used for?
What is in the form of liquid lipids and solid lipids?
What elements does lipids include?
Solubility?
Are they polymers?
Characteristics?`

Answer 23

Some lipids are used for energy storage (fats) but a large fraction of cellular lipids are used to form lipid membranes.
Liquid lipids - oils
Solid lipids - fats
- Contain C,H and O (very low proportion is O)
- Insoluble in water but soluble in organic solvents *alcohol and acetone)
- Not polymers - they are small molecules that associate through non covalent forces
- Usually characterised by the kind of structure where they have a polar hydrophilic head and non polar hydrophobic tail

Question 24

What is the purpose of fat covering organs? Where is it bad to have too much fat around?

Answer 24

The fat covering organs help thermoregulation. Too much can block blood flow. As long as the fat is not around vital core organs, it is safe because they wont interfere with the function

Question 25

What are the functions of lipids? (8)

Answer 25

1) source of energy – provide more than twice as much energy as carbohydrates when oxidized
2) Storage energy – adipose cells and tissues
3) biological membranes
4) insulation – blubber and electrical insulation
5) protection – cuticle on plants to prevent water loss and fatty layer surround organs
6) hormones (steroid hormones) are stored as lipids
7) buoyancy – the pits are less than water – aquatic animals and birds (oil droplets)
8) waterproofing – insoluble in water

Question 26

What is one of the principal groups of lipids?
What can lipids be categorized as? (3)
Fats and oils - liquid or solid?

Answer 26

Triglycerides (i.e. fats in adipose tissue in humans and the oil in sunflower seeds).

Lipids can be categorized as fats, oils and waxes. Fats are solid at room temperature but liquid at body temperature. Oils are liquid at both temperatures.

Question 27

How are triglycerides formed?
How many condensation reactions? Water produced?
What are the bonds called? What type of bond is it?

Answer 27

• Triglycerides are formed by condensation from free fatty acids and one glycerol.
• Each fatty acid is bonded to the glycerol molecule in 3 condensation reactions therefore 3 water molecules are produced.
• the covalent bonds are known as Ester bonds that form when a reaction occurs between the -COOH groups of the fatty acids and the -OH groups of the glycerol molecule.

Question 28

What are lipids? How are triglycerides lipids?

Answer 28

Lipids are the sole combine with one, two or three fatty acids. Therefore triglycerides are lipids

Question 29

How are the lipids more suitable for long-term storage in humans than carbohydrates?

Answer 29

Organisms can store energy in the form of carbohydrates and/or lipids

Living organisms tend to use carbohydrates as a in the short term energy storage while lipids are used as the long-term energy storage.

• lipids contain 9 cal per gram whereas carbohydrate molecules only carry 4 cal per gram. This means that lipid stores are less dense (less body mass) for the same amount of energy from carbohydrates.
• stored lipids form pure droplets whereas carbohydrates are stored with water so lipids are 6x more efficient than carbs in the amount of energy that can be stored per gram of body mass

Question 30

How are lipids used in structure, hormonal signaling, insulation, protection and storage of energy?

Answer 30

Structure:
phospholipids are a main component of cell membranes

Hormonal signaling: steroids are involved in hormonal signaling (i.e. estrogen, progesterone, testosterone)

Insulation: that’s an animals conserve as he insulators while sphingolipids in the myelin sheath (of neurons) can serve as electrical insulators

Protection:
triglycerides may form a tissue layer around many key internal organs and provide protection against physical injury

Storage of energy: triglycerides can be used as a long-term energy storage source

Question 31

How do lipids and carbohydrates compare in terms of role, efficiency, accessibility and use for respiration?

Answer 31

• Store lipids can also act as insulators. Carbohydrates do not have a secondary role
• living organisms are able to digest carbohydrates easier and more efficiently than lipids which means that the energy stored in the molecule can be released faster. =carbs better for short term
• it is more difficult for lipids to be mobilized and use inside respiration and carbs. They are nonpolar and can only be used in aerobic respiration whereas carbohydrates are polar, can be transported easily and can be used in both aerobic and anaerobic respiration.

Question 32

What is the structure of fatty acids?

Answer 32

Fatty acids have a carbon chain with hydrogen atoms attached by a single covalent bond forming a hydrocarbon chain. There is a carboxyl group attached at the end of the chain which is the acid component of the fatty acid.

Question 33

How do fatty acids differ?

Answer 33

• They differ in the number of carbon atoms in the hydrocarbon chain. Most half between 14 and 20 carbon atoms in the chain.
• the bonds that form between the carbon atoms (Some are single bonds between the carbon atoms leaving room for two hydrogen atoms to bond to the carbon while others are double bonds leaving less room for hydrogen atoms)

Question 34

What are saturated fatty acids? Why are they considered saturated fatty acids?

Answer 34

• Saturated fatty acids are composed of all single covalent bonds between the carbon atoms.
• They are considered saturated fatty acids because they hold a maximum amount of hydrogen atoms possible.

Question 35

What are unsaturated fatty acids? Why are they considered unsaturated?

Answer 35

Unsaturated fatty acids contain one or more double bonds between carbon atoms in a hydrocarbon chain.
They contain less hydrogen than they could hold so they are considered unsaturated.

Question 36

Unsaturated fatty acids can be cis or trans isomers. What is the difference between the two?

Answer 36

Cis-isomers

• very common in nature
• the hydrogen atom are on the same side of the two carbon atoms
• the double bond causes a bend in the fatty acid chain
• therefore cis-isomers are only loosely packed
• Triglycerides form from cis-isomers have low melting points - usually liquid at room temp

Trans-isomers

• Rare in nature - usually artificially produced to produce solid fats
• the hydrogen atoms are not on the same side of the two carbon atoms
• double bond does not cause a bend in the fatty acid chain
• Trans-isomers can be closely packed
• triglycerides formed from trans-isomers have high melting points - usually solid at room temp

Question 37

What is the correlation between saturated fatty acid intake and rates of CHD?

Answer 37

postive correlation

Question 38

What is the correlation between amounts of trans-fat consumed and rates of CHD?

Answer 38

positive correlation

Question 39

What does a correlation not prove?

Answer 39

a causation